The present invention relates generally to operations performed in a subterranean well and, in an embodiment described herein, more particularly provides a formation testing apparatus and associated methods of testing a formation.
It is well known in the subterranean well drilling and completion arts to perform tests on formations intersected by a wellbore. Such tests are typically performed in order to determine geological and other physical properties of the formations and fluids contained therein. For example, by making appropriate measurements, a formation's permeability and porosity, and the fluid's resistivity, temperature, pressure, and bubble point may be determined. These and other characteristics of the formation and fluid contained therein may be determined by performing tests on the formation before the well is completed.
It is of considerable economic importance for tests such as those described hereinabove to be performed as soon as possible after the formation has been intersected by the wellbore. Early evaluation of the potential for profitable recovery of the fluid contained therein is very desirable. For example, such early evaluation enables completion operations to be planned more efficiently.
Where the early evaluation is actually accomplished during drilling operations within the well, such as during a wiper trip, the drilling operations may also be more efficiently performed, since results of the early evaluation may then be used to adjust parameters of the drilling operations.
In typical formation testing equipment suitable for interconnection with a drill string during drilling operations, various devices and mechanisms are provided for isolating a formation, or portion of a formation, from the remainder of the wellbore, drawing fluid from the formation, and measuring physical properties of the fluid and the formation. For isolating the formation and drawing fluid from the formation, separate mechanisms are generally provided. For example, a pad having a seal element thereon and a fluid passage formed therein may be pressed against the formation and a piston within a sampling tool may be displaced to cause fluid to flow from the formation into the fluid passage. Unfortunately, these mechanisms are usually relatively complex and expensive to manufacture, and require manipulation of the drill string to displace the piston, etc.
Therefore, it would be quite desirable to provide a method of performing an early formation evaluation test, which does not require separate formation isolation and fluid pumping mechanisms, and which does not require manipulation of the drill string to perform either of these functions. Furthermore, it would be desirable to provide an apparatus which is usable to perform the method, and which may be used to inject fluid into the formation, for example, to stimulate the formation. It is, thus, an object of the invention to provide such methods and apparatus.